Since the discovery of the vasoactive effects of glyceryl trinitrate (also referred to as nitroglycerin), compounds containing nitrate or nitrite esters groups have been used in the treatment of various cardiovascular disorders such as, angina pectoris, congestive heart failure and myocardial infarction. See Parratt, J. R., J. Pharm. Pharmacol., 31, 801 (1979). The utility of these compounds arises from their ability to release nitric oxide (NO). See Ignarro, L. J., Pharmacology and Pharmaceut. Res., 6, 651 (1989). NO is believed to activate a soluble form of guanylate cyclase, a cellular enzyme, which catalyses the formation of 3',5' cyclic guanosine monophosphate (cGMP). See Kamm, et al., Annu. Rev. Physiol., 51, 299 (1989). It is the action of cGMP on other cellular targets that is thought to mediate relaxation of vascular smooth muscle and provide the therapeutic effect of nitrovasodilators.